Biological factors are generally viewed as important determinants of both normal and pathological behavior, including aggression, in animals and humans. The brain is recognized to be the behavioral control center, consequently it makes sense that damage or dysfunction in this organ should be associated with behavior disorder. Although biological models of generalized aggression abound, the role of biological factors in marital aggression has been virtually ignored. In the parent project, a strong association between head injury an marital aggression has been found. Head injured men were found to be significantly more likely to be abusive of their wives than non-head injured men. The aim of the proposed investigation is to both extend and broaden the examination of biological factors as they relate to marital aggression. Two studies are proposed. The first, a prospective, longitudinal study of head-injured men, from the point of head injury, will examine the development of marital discord, anger and aggression in the two years post-injury. The Cox proportional hazards model will be used to account for the time interval from injury to a maritally aggressive event. The neuroendocrine system, especially the neurotransmitter Serotonin, has been implicated in the etiology of aggression. Study 2 will evaluate the serotonergic function of abusive males using Prolactin response to fenfluramine challenge as the index of serotonergic activity. It is expected that batterers will have reduced serotonergic activity compared to non-abusive controls. Marital aggression is a significant health problem in the U.S. Treatment prevention of marital aggression is an important health priority. Inattention to biological variables cuts off potentially important avenues for attaining these goals. The proposed studies will greatly increase and refine our understanding of the role of these factors in marital aggression and could lead to significant biological treatments (or adjuncts to current clinical approaches).